This invention relates to tires, and more particularly to an improved pitching sequence for the tread portion of a tire.
The tread portion of a tire comprises a plurality of design cycles placed continuously about the circumference of the tire. For any particular tread pattern, a certain amount of energy is produced in the form of sound, which can take the form of a harsh and disagreeable noise. Various methods have been suggested in the prior art to reduce objectionable noise generated by tires by spreading the energy produced over the frequency spectrum. The primary method used is to modulate the length of the repeating design cycle by varying the length of the design cycle about the circumference of the tire. This is generally known in the prior art as pitching. Generally three different design cycle lengths are arranged in some sequential order about the circumference of the tire. However, the pitching of the design cycles can itself cause objectionable noise.
The objectionable noise generated by tires of the prior art resides generally in either the loudness, i.e. decibel level, or tonality, the concentration of too much energy into anyone particular frequency. This becomes of even more importance in tires having aggressive tread patterns, for example tires primarily designed to be used as a snow tire or in all weather conditions.
Applicants have developed a novel pitching arrangement whereby the decibel level and tonality of the tire is reduced. For the purposes of this invention, tonality is the condition wherein the sound generated by the tread portion of the tire is dominated by a single frequency and its harmonics, that is, the majority of the sound generated being concentrated into a very small frequency range of the sound spectrum.